Lonely Koalas Long Ago Turned to Kin for Sex

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A checkered past for Australia's koalas means that the tuft-eared
marsupials have low genetic diversity — a sign of inbreeding.

Mating with kin is not unusual in animals with declining
populations, and researchers expected to find that the koalas
(Phascolarctos cinereus) had been doing just that. But
scientists were surprised to learn how far back the inbreeding
goes.

"We thought that, like other species, such as the gray
wolf, where the population has recently declined, there
should be greater diversity in museum samples than modern
specimens," because museum samples come from an earlier era, said
Alex Greenwood, a researcher at the Leibniz Institute for Zoo and
Wildlife Research in Germany.

"We found this not to be true," Greenwood said in a statement.
"The event which reduced the genetic diversity of koalas must
have happened a long time ago."

Europeans arriving in Australia in the late 1700s first noted
that koalas were rare, perhaps because of Aboriginal hunting. By
the mid-1800s, declines in hunting put koalas on the rebound, but
then the species' fortunes once again soured. Koala fur became a
fashionable accessory, and hunting again drove the species to the
brink. Habitat loss and
disease, particularly Chlamydia, also threaten today's
koalas.

The Australian government lists the species as "vulnerable," and
the U.S. government classifies them as "threatened." Low genetic
diversity means that koalas may struggle to adapt to changing
climate conditions or new diseases.

Greenwood and his colleagues compared modern
koala DNA with that of 14 museum specimens. They focused on
mitochondrial DNA, which is the genetic code found in the part of
the cell that converts energy for the cell's use. Mitochondrial
DNA is inherited from the mother.

Although the old, museum specimens came from different regions
and different points in time, their genetic profiles did not
differ from today's specimens. That means that the loss of
genetic diversity in koalas did not occur recently, Greenwood
said.

It's possible, he added, that the loss dates as far back as the
late Pleistocene, when the giant koala (Phascolarctos
stirtoni) went extinct. Giant koalas were about a third
larger than today's and died off out about 50,000 years ago.